1. Field of the Invention
The present invention relates to methods and compositions for the topical treatment of neuropathy. More particularly, the present invention relates to transdermal compositions including a combination of ingredients that provide a surprising degree of effective relief from the symptoms of neuropathy and to methods for administering topical compositions to treat neuropathy.
2. Description of the Prior Art
Peripheral neuropathy is a condition involving nerve-end damage anywhere in the body. Peripheral neuropathy generally refers to a disorder that affects the peripheral nerves, most often manifested as one or a combination of motor, sensory, sensorimotor, or autonomic neural dysfunction. The wide variety of morphologies exhibited by peripheral neuropathies can each be uniquely attributed to an equally wide variety of causes. For instance, peripheral neuropathies can be genetically acquired, can result from a systemic disease, can manifest as a post-surgical complication, or can be induced by a toxic agent. Some toxic agents that cause neurotoxicities are therapeutic drugs, antineoplastic agents, contaminants in foods or medicinals, and environmental and industrial pollutants.
Neuropathy is a major complication of diabetes mellitus. No well-established treatments exist for either its symptomatic treatment or for prevention of progressive decline in nerve function. Estimates of the prevalence of neuropathy in diabetes vary widely, from a low of 5% to a high of 80%, largely due to the numerous definitions and clinical descriptions of neuropathy. Nevertheless, the additive effects of neuropathy in the suffering diabetic patient are well known and documented. The effect of the neuropathy is complex. The loss of sensory information from the foot is related to abnormal and prolonged pressure on the areas of the foot (sensory neuropathy). Motor neuropathy leads to deformity, further increasing pressure loading on the foot. In autonomic neuropathy, loss of innervation of the sweat glands results in dry skin that cracks creating an environment amenable to infection. Autonomic dysfunction contributes further by altering the distribution of micro-circulatory blood flow, directing the blood flow through shunts and away from the nutritive skin capillaries. These factors as a whole, in conjunction with foot trauma, result in skin breakdown and ulcers.
Scientists have not yet determined the mechanism that leads to nerve damage in diabetes, but it is believed to be multifactorial. These factors include genetic predisposition, metabolic and vascular abnormalities, and lack of perturbation of growth factors. The response of the peripheral nervous system to the metabolic effects of diabetes does not appear to differ between type 1 and type 2 diabetes, which suggests a likelihood of similar clinical response to therapies in the two primary forms of the disease. There seem to be a number of susceptibility factors, as yet unknown, for the development of neuropathy, which operate in the presence of hyperglycemia (high blood sugar).
Although a number of neuropathies are related to the disease diabetes mellitus, others, although not known to be related to diabetes are similar in their physiological effects on the peripheral vascular system. Such diseases include Raynaud's Phenomenon, including CREST syndrome, autoimmune diseases such as erythromatosis, and rheumatoid diseases. Other peripheral neuropathies include the following: HIV associated neuropathy; B12-deficiency associated neuropathy; cranial nerve palsies; drug-induced neuropathy; industrial neuropathy; lymphomatous neuropathy; myelomatous neuropathy; multi-focal motor neuropathy; chronic idiopathic sensory neuropathy; carcinomatous neuropathy; acute pain autonomic neuropathy; alcoholic neuropathy; compressive neuropathy; vasculitic/ischaemic neuropathy; mono- and poly-neuropathies.
For example, among the most important toxic agents causing peripheral neuropathy are therapeutic agents, particularly those used for the treatment of neoplastic disease. In certain cases, peripheral neuropathy is a major complication of cancer treatment and is the main factor limiting the dosage of chemotherapeutic agents that can be administered to a patient (Macdonald, Neurologic Clinics 9:955-967 (1991)). This is true for the commonly administered agents cisplatin, paclitaxel and vincristine (Broun, et al., Am. J. Clin. Oncol. 16:18-21 (1993); Macdonald, Neurologic Clinics 9:955-967 (1991); Casey, et al., Brain 96:69-86 (1973)). The identification of methods for preventing or alleviating dose-limiting peripheral neuropathologic side effects would allow higher, and more therapeutically effective doses of these chemotherapeutics to be administered to patients, i.e., the therapeutic efficacy of such chemotherapeutics is typically a function of dose and therefore, increasing dosage provides increased patient survival (Macdonald, Neurologic Clinics 9:955-967 (1991); Oxols, Seminars in Oncology 16, suppl. 6:22-30 (1989)).
Tragically there is no existing method for adequately, predictably and specifically treating established neuropathic pain (Woolf C. et al., Neuropathic Pain: Aetiology, Symptoms, Mechanisms, and Management, Lancet 1999; 353: 1959-64). Present treatment methods for neuropathic pain consists of merely trying to help the patient cope through psychological or occupational therapy, rather than by reducing or eliminating the pain experienced.
Currently, there are a limited number of drugs available for the treatment of neuropathy. Most treatments composition and methods are directed towards relief of pain. Currently, there are several categories of treatments utilized, including medical procedures and drugs, which are provided locally or systemically. For example, current methods to treat neuropathic pain include administration of local anesthetic blocks targeted to trigger points, peripheral nerves, plexi, dorsal roots, and to the sympathetic nervous system. However, these treatments have only short-lived antinociceptive effects. Additionally, longer lasting analgesic treatment methods, such as blocks by phenol injection or cryotherapy raise a considerable risk of irreversible functional impairment. Furthermore, chronic epidural or intrathecal (collectively called “intraspinal”) administration of drugs such as steroids, opioids or midazolam have significant side effects and questionable efficacy. Medical procedures are ineffective and often expensive, leading to various pains that many times supercede the original pain.
The current standard of practice for the non-invasive treatment of the various neuropathies include the following drug classes: (1) The Non-Steroidal Anti-inflammatory Drugs (NSAIDs); (2) Narcotic analgesics; (3) Tricyclic antidepressants; and (4) Anticonvulsants, e.g., carbamazepine and gabapentin. These classes are available commercially as oral products and, generally, are administered via the oral route. Because they are distributed systemically throughout the body, their various side effects limit their effectiveness. The NSAIDs, for example, when taken orally cause gastric distress—including ulcers. The other three classes share other common side effects, including drowsiness, dizziness, disorientation, and gastrointestinal upset to name but a few.
Several topical agents (creams, ointments, liniments and the like) have been utilized for the relief of the pains and aches of neuropathies. Most of these have provided a little, but only temporary, relief to persons suffering from pain. Many combinations of varying ointments, creams, aqueous solutions, liniments and the like for the treatment of neuropathies have been employed. The most efficacious of these contains as its active ingredient the vegetable products derived from the seed and pods of the capsicum plant, commonly known as red pepper. Capsicum-derived ointment is devised for external application to the affected area of the body by applying to the area adjacent to the muscle, joint or tendon and rubbing it into the skin. The active ingredient is capsaicin. With initial as well as persistent application, capsaicin is effective to relieve the aches and pains of various muscle or skeletal origin, such as arthritis, muscle strains, tendonitis, bursitis and soft tissue diseases.
U.S. Pat. No. 5,665,360 (Mann) relates to the treatment of peripheral neuropathies associated with diabetes mellitus by periodic topical application of a composition containing capsaicin as the active ingredient. When applied to the skin of the affected area, pain and burning associated with the neuropathy are said to be reduced. However, capsaicin has been shown to kill nerve endings in some cases and is extremely irritating to the dermis. Thus this composition suffers from these disadvantages.
The use of ketamine transdermally in an organogel has shown some promise in the treatment of neuropathy. Ketamine is an N-methyl-D-aspartate receptor antagonist and thus blocks a cascade of intracellular events that inhibit the hyper excitability of spinal cord neurons. Animal data show that certain spontaneous pains and allodynia have been treated successfully with Ketamine. Also, in humans, phantom limb pain has been treated with success (Nadine & Bouhassira, Acta. Neurol. Scand 1999 (Supp 173):12-24). Ketamine has been used experimentally to treat neuropathic pain by a variety of routes including the intravenous and subcutaneous. The topical form of Ketamine is effective in treating painful neuropathy when other traditional medicines have failed. (Crowley et al., International Journal of Pharmaceutical Compounding 1998; 2:122-1273).
Other compositions have been employed, including combinations of individual compounds. U.S. Pat. No. 6,387,957 B1 (Frome) relates to the treatment of Sympathetically Mediated Pain (SMP), which include various neuropathies, employing the compounds ketamine (NMDA receptor antagonist), amitriptyline (anticholinergic antidepressant), and guanethidine (sympathetic blocking agent), in combination or independently. However, the compounds employed by Frome act independently of each other as illustrated by the effectiveness of individual compounds. Frome's invention lacks any synergism of the compounds as the compounds merely complement the other compounds, but does not synergize, or supplement, the activities of the other compounds. For example, ketamine a very potent antineuropathic agent was used in limited concentrations. Whether alone or in combination, small concentrations of ketamine were likely used due to ketamine's known neurotoxic effects. Frome's invention also suffers from limitations in the preparation, dosage, application or administration methods and potential side effects. The effectiveness of Frome's compounds depends on the volume of the preparation and whether the compounds are alone or in combination. The side effects of amitriptyline and guanethidine are well known. These are disruptive to a person's quality of life and are not addressed by Frome in his patent.
Accordingly, there remains a need in the art for effective treatments for neuropathies, and other neuropathic pains.